1. Field
The following description relates to multi-wavelength optical transmitting and receiving modules which can be used to multiplex and demultiplex optical signals of multiple wavelengths.
2. Description of the Related Art
An increase in data traffic resulting from the advancement of the Internet is increasing the speed and volume of optical communication networks. For transmission of high-volume data traffic, wavelength division multiplexing (WDM) is widely used. WDM is a technology that multiplexes optical signals having different wavelengths on a single optical fiber. WDM has been used mainly in backbone networks but has also been applied in access loop networks and Ethernet networks.
In the case of 40 gigabit (G) Ethernet, 10 G×4 channel coarse wavelength division multiplexing (CWDM) has been adopted as a standard for transmission over a 10 km single-mode fiber. In the case of 100 G Ethernet, 25 G×4 channel local area network (LAN)-WDM has been adopted as a standard for transmission over a 10 km or 40 km single-mode optical fiber.
In 40 G and 100 G Ethernet, an optical transmitting and receiving module multiplexes four channels and transmits the multiplexed channels. Key parts of the optical transmitting and receiving module include a transmitter optical sub-assembly (TOSA) and a receiver optical sub-assembly (ROSA). The TOSA performs electrical-optical conversions of four channels and wavelength multiplexing, and the ROSA performs wavelength demultiplexing and optical-electrical conversion of the four channels.
FIG. 1 is a cross-sectional view of a conventional optical transmitting and receiving module 10 (disclosed in U.S. Patent Application No. 2004-971462).
Referring to FIG. 1, the optical transmitting and receiving module 10 is configured to have the function of the ROSA. When optical signals of multiple wavelengths are incident upon thin-film filters 12a through 12d, which are arranged in a pentagon, through a receptacle 11, each of the thin-film filters 12a through 12d allows only an optical signal having a corresponding wavelength to pass therethrough and reflects optical signals having the other wavelengths. Optical signals λ1, λ2, λ3, and λ4 that pass through the thin-film filters 12a through 12d are input is to photodetector devices 13a through 13d and are there converted into electrical signals.
If the optical transmitting and receiving module 10 is configured to have the function of the TOSA, the photodetector devices 13a through 13d may be replaced by laser diode devices. In this case, optical signals of multiple wavelengths may be output from the laser diodes. When the optical signals output from the laser diodes are input to the thin-film filters 12a through 12d, each of the thin-film filters 12a through 12d may allow only an optical signal having a corresponding wavelength to pass therethrough and reflect optical signals having the other wavelengths. The reflected optical signals may be output through the receptacle 11.
In the optical transmitting and receiving module 10 structured as described above, parts to or from which electrical signals are input or output are scattered over multiple locations and in multiple directions. Thus, it may be very difficult to design an electrical signal interface and reduce the size of the optical transmitting and receiving module 10.
FIG. 2 is a cross-sectional view of another conventional optical transmitting and receiving module 20 (disclosed in U.S. Pat. No. 6,198,864).
Referring to FIG. 2, the optical transmitting and receiving module 20 is configured to have the function of the ROSA. A series of concave relay mirrors 22a through 22c are integrated into an optical block 21. When optical signals of multiple wavelengths are incident upon the optical block 21 through an optical fiber 23, each of filters 24a through 24d allows only an optical signal having a corresponding wavelength to pass therethrough and reflects optical signals having the other wavelengths. The optical signals propagate while this process is repeated. The optical signals that sequentially pass through the filters 24a through 24d are input to photodiodes 25a through 25d and are there converted into electrical signals. Light reflected by the filters 24a through 24d is continuously focused by the relay mirrors 22a through 22c. 
For single-mode reception, a light-receiving region of a photodiode is tens of μm in diameter. For single-mode transmission, a diameter of a core of an optical fiber is approximately 8 μm. Thus, the presence of a manufacturing error in the optical transmitting and receiving module 20 may result in a large loss of optical signals. In addition, since the optical transmitting and receiving module 20 using the relay mirrors 22a through 22c has a lower alignment tolerance than an optical transmitting and receiving module using lenses, a significant alignment-related optical loss may occur, thereby deteriorating mass productivity.